The objective of this research is to find controlling mechanisms in the growth of animal cells. We have found several clones of cells isolated from tumor virus-transformed cell lines which have regained entirely normal control of DNA synthesis in monolayer culture which still retaining the tumor virus genome. We hope to elucidate the mechanism of growth control in these cells by biochemical means including the use of restricton endonucleases to describe host DNA sequnces adjoining the viral genes and the use of DNA-RNA hybridization to measure the extent of viral gene expression. In related work we have been able to isolate nuclei from these and other cells using a radical non-aqueous isolation procedure. The nuclei retain the ability to synthsize RNA andDNA in the test tube. We hope to find controlling elements in both RNA and DNA synthesis by studying factors which affect cell-free synthesis.